1. Field of the Invention
The present invention relates to a boat lift, and more particularly, to a boat lift that uses the boat's propulsive force to lift the boat from the water.
2. Description of Related Art
Recreational boat owners can spend large amounts of time and money on maintenance and repair of their vessels. Leaving a boat or other craft in water for long periods can cause build up on the hull of algae (in fresh water) and barnacles (in salt water), and can cause pits and other surface imperfections in common hull materials like fiberglass and wood. Maintenance of a boat hull left in water can require significant expenditures of time and money. Rather than using labor-intensive and often costly approaches such as specially formulated paints or other surface treatments, many boat owners elect to keep their boats out of the water when not using them.
There are many types of boat lifts suitable for removing boats from the water. One example uses a structure that is first positioned beneath the hull of the boat and then lifted by cables. This type typically employs an electric motor to supply the necessary lifting force, but it can be operated manually as well. A variation uses a screw drive rather than cables. Another lifts a boat-supporting structure using buoyancy forces exerted upon the structure by large tanks or inflatable bladders filled with air by electric pumps. Other known devices use hydraulic actuators to drive mechanical links or cables to lift the boat. Another type of boat lift uses a buoyant structure that serves as the boat's dock, and the boat powers itself up and onto this buoyant structure. This type device is most useful with small “personal water craft,” because it is more difficult to launch larger boats from this type of docking device.
The following patents illustrate a number of boat lifts that incorporate some of the above approaches:                U.S. Pat. No. 4,037,421 U.S. Pat. No. 5,090,841        U.S. Pat. No. 4,808,028 U.S. Pat. No. 5,485,798        U.S. Pat. No. 4,832,210 U.S. Pat. No. 5,860,379        U.S. Pat. No. 4,934,298 U.S. Pat. No. 6,006,687        U.S. Pat. No. 5,051,027        
Boat lifts that operate manually are burdensome and slow, and all boat owners may not be capable of using them. On the other hand, electrically or hydraulically operated lifts require the ready availability of electrical power or pressurized fluid at the boat dock. In addition, they typically operate slowly, and can take undue time for both docking and launching the boat. Increasing the operational speed of electrically or hydraulically powered boat lifts can require the use of inordinately large equipment and amounts of electrical power. Conventionally, a boat lift that relies on the boat to power itself up and onto a buoyant structure would likely have limited utility for larger boats, which would require flotation devices with a relatively large surface area to achieve the necessary buoyancy. This could make such devices incompatible with covered docks that have limited available space. Likewise, launching large, heavy boats docked with such devices is more difficult, as well.
In short, there are myriad boat lift permutations incorporating one or more of the features discussed above. However, none is completely satisfactory as a boat lift for many existing types and sizes of boats and other water craft, nor are they all adaptable for use with different configurations and sizes of docks.